This invention relates to the field of electro-optical detecting apparatus which utilizes "mosaic" detector arrays to provide surveillance of an extensive scene. The mosaic detector arrays are large numbers of closely-spaced individual photo-detector elements arranged in essentially a two-dimensional, or planar, array. The present invention is specifically concerned with a method, and resulting product, in which the photo-detectors are emplaced on, and integrated with, the supporting structure, the supporting structure containing electrically-conducting leads which are exposed as spaced contact points on the focal plane of the structure and which are intended to be individually in electrical contact with separate photo-detectors.
An earlier patent application of Carson and Dahlgren, Ser. No. 855,242, filed Nov. 28, 1977, and assigned to the assignee of this application, discloses a detector module comprising a number of thin insulating layers, or substrates, secured together and extending at right angles to the focal plane of the detector array. Electrically-conducting leads are supported by and located between such layers for the purpose of conducting signals away from the detectors located in the focal plane. The pre-fabricated layered supporting structure thus constitutes the substrate for the detector array. The earlier application refers to the step of "detector integration", wherein "the photo-detectors are emplaced on the focal plane end of the module, in contact with the thin film conductors formed between the thin module layers." Reference is made in that application to "a proprietary process of the assignee of this application" which was developed with particular reference to the use of mercury-cadmium-telluride detectors.
The present application relates to the process referred to in the prior application, but its usefulness is not limited to mercury-cadmium-telluride (HgCdTe) detectors.
Great difficulty has been encountered in satisfactorily emplacing detectors on the focal plane face of the supporting module. The requirements are very stringent because the goal is to end up with thin diode chips attached to the end of the module and in electrical contact with the lead points on the module. Thus, each detector must be separately in electrical contact with an individual electrical lead in the supporting module. This means that the detectors, which are very small and very closely located, must be electrically isolated from one another, and must each be located on top of one of the thin film electrical leads. The chances for the fabrication to fail are extremely high. To the best of the applicant's knowledge, present fabrication method is the first successful effort to deal with the complex and frustrating problems involved.
Previous efforts to emplace detectors on a supporting structure having conductor contact points on its surface have involved using detectors in which p-n junctions have been previously formed and separated into mesas, and securing the detectors to the supporting structure in electrical contact with the conductor end points by placing minute solder bumps on the individual points and aligning the mesas with the solder bumps as the detector material is placed against the supporting structure.
The accompanying Prior Art Statement includes additional information concerning the efforts to integrate focal plane photodetectors.